ET stands for elapsed time. It is a program to measure the time taken to
run another program or a DOS command. For example, if you have a program
called HANOI somewhere on your path, and you want to measure the time
that it takes to execute, type
  ET HANOI
at the DOS prompt. You can include parameters after the program name as
you would normally do. The timed program can ask you questions and wait
for you to type responses, but of course this introduces variability into
the elapsed time.

Two points to note:

1/ ET runs your program in a sub-shell which means that it must create a
   second version of COMMAND.COM. To do this it must be able to find
   COMMAND.COM. You MUST have an environment variable COMSPEC which tells
   ET where to find it, even if it is in the root directory. For example,
     SET COMSPEC=C:\DOS\COMMAND.COM
   If you have a floppy-only machine then of course you must have a floppy
   containing COMMAND.COM in one of the drives.

2/ ET is accurate to about 0.1 seconds. This seems to be a DOS limitation.
   For good accuracy you should have both the program which you wish to
   time and COMMAND.COM (as specified by COMSPEC) in RAM disk. ET itself can
   even be on floppy disk, since of course it only starts measuring time
   after it has been loaded into memory.